An on-screen display (OSD) menu is widely used for operation and controlling a plurality of computers through a keyboard-video-mouse (KVM) switch or accessing one computer from a plurality of consoles via a console sharing device. Users can select any one of the pluralities of computers from the OSD menu present on a display of a console or send commands to the computer to access the computer from one of the consoles. Users can know the operation status of the computers from the OSD menu. Therefore, an on-screen display (OSD) circuit has been widely utilized to be almost a standard component inside the keyboard-video-mouse (KVM) switch or the console sharing device for remote accessing to the computer. However, the design of the KVM switch or the console sharing device has greatly been improved on aspects of functions. The number of computers joined to the KVM switch or the console sharing device has been greatly increased, particularly mentioning about the matrix KVM switch connecting a plurality of computers and a plurality of console devices. The circuitry integration inside the KVM switch is getting necessarily complicated with the great improvement for various functions and the increased number of the joined computers of the KVM switch.
Up to the present, all the on-screen display (OSD) circuits are built in the KVM switch, in the I/O module or the console module coupled to the KVM switch without any exception. The OSD circuit, which generates the OSD menu signal for the KVM switch or the console sharing device is quite related with the video signal processing of the jointed computers. When the length of the cable interconnecting between the KVM switch and console device (or the jointed computer) is extended, the magnitude of the video signal from the jointed computers might decay with the extension of the length of the cable due to the high frequency of the video signal transmission rate. Therefore, it is necessary to re-design the on-screen display (OSD) circuit for matching the video signal processing in the KVM switch system (the KVM switch, the I/O module or the console module coupled to the KVM switch) which is integrated into the main circuitry of the KVM switch even the main circuitry of the KVM switch, the I/O module or the console module is re-designed only little.
Furthermore, when the combing of the analog OSD menu signal and the analog video signal from the jointed computer is processed inside the KVM switch, the analog video signals are easily interfered by the electromagnetic field (EMF) generated by other circuits, especially the EMF generated by the high-frequency digital signal circuits. Thereupon, an abnormal, bothersome display caused by aforementioned interference can be observed on the display.
Moreover, in case the KVM switch without on-screen display (OSD) circuit thus without an OSD function is attempted to be upgraded to own the OSD function, it has to take much more effort and much more consideration to re-design the hardware circuit of the KVM switch to accommodate an OSD circuit and also delete interference caused by the electromagnetic field (EMF) generated by other circuits when re-designing the on-screen display (OSD) circuit for matching the video signal processing in the KVM switch system can not be avoided.
The OSD menu signal processing is more related with the standard of Video Graphics Array (VGA), Digital Visual Interface (DVI) or other standard for the extended developments of video signal process but not the KVM switch circuitry. Nowadays, an on-screen display (OSD) circuit is mostly embedded in the KVM main circuitry design. Such on-screen display circuit, which is built in the KVM main circuitry design is disclosed in U.S. Pat. No. 5,721,842 or its continuation applications, such as U.S. Pat. No. 6,112,264. The OSD circuit is as aforementioned to be arranged in the KVM switch, in the I/O module or the console module coupled to the KVM switch without exception. With the development of KVM switch, the on-screen display (OSD) circuit embedded inside has to be tuned up with the KVM switch main circuitry to have the perfect video signals without interference on the display when the KVM switch design is altered, for example: for meeting the different distances for coupling to the computer and console device, for increasing the capability of the number for jointing computers or consoles, for adding more extra-functions of KVM switch, for upgrading the KVM signals switching, KVM signals transmission performance between the computers and console. Each time, tuning the on-screen display (OSD) circuit with the KVM switch main circuitry becomes a must for the alteration of the KVM switch main circuitry, not to mention about a great tuning, the re-designing the on-screen display (OSD) circuit for matching the video signal processing in the KVM switch system when the KVM switch without OSD function is attempted to be upgraded to own the OSD function.
Furthermore, the types and purposes of KVM switch design by far could be hundreds, even thousands; therefore, it cost lots effort for reworking of the OSD circuit tuning. An OSD system located externally the KVM switch system or the console sharing device can solve kinds of problems mentioned above. The external OSD system can combine the video signal of the computer and the on-screen display menu signal or overlap the on-screen display menu signal on the video signal from the computer outside the KVM switch system (outside the KVM switch, outside the I/O module or the console module coupled to the KVM switch). Even though the KVM switch is re-designed, the OSD system remains focusing on the video signal processing without tuning with the KVM switch circuitry for each time. When the cable length between the KVM switch and console device extends, re-designing the OSD system for cable length is much simpler and much easier than redesigning the whole KVM switch and tuning the OSD circuit with. Even the KVM switch without OSD circuit is attempted to be upgraded to own the OSD function, the great tuning, the re-designing for the on-screen display (OSD) circuit in the KVM switch system is effortlessly completed.
Correspondingly, there is a need to develop an on-screen display (OSD) circuit separately from a keyboard-video-mouse (KVM) switch or a console sharing device for simplifying the structure of the circuitry therein and provide an on-screen display cable combining a video signal of a computer and an on-screen display menu signal or overlapping the on-screen display menu signal on the video signal.